In oil well operations the need occasionally arises for the introduction of tools or equipment into a pressurized well for a variety of purposes including internal pressure and temperature surveying, swabbing and removing water, and, most importantly, fishing or the locating and retrieving of broken and/or stuck tools.
The problem of broken and/or stuck tools is particularly bothersome in that unless such tools can be removed through fishing, retrieved by the lowering of grappling equipment by cable through the well, the well must be killed, that is sealed off at the bottom, after which the broke or stuck pieces are removed using drilling equipment. This is an extremely time-consuming and expensive procedure.
A major factor in the operability of the fishing equipment is the ability to move the equipment down the well against the internal pressure. Under ideal circumstances, this can be effected by weighting the cable, mounting weights thereon sufficient to, in conjunction with the weight of the equipment and the cable itself, move the cable downward to the desired location. However, because of a combination of factors including well pressure, cable strength and cable size, this is frequently not possible. Basically, when the well pressure exceeds a certain point, which varies under different circumstances, overcoming the pressure merely by the use of weights on the cable will not work. A factor contributing to this problem is that while the larger the cable used, the greater the weight that can be suspended therefrom and the less likelihood of breakage or loss of the cable down the well, the larger cable, having a greater diameter, presents a substantially greater surface against which the well pressure bears. In other words, the larger the cable, the more the pressure resists its passage into the well.
The above problem cannot be solved solely by the addition of more weights in that the weights are of necessity limited in size to be accommodated within the well pipe. Further, there is normally a limited height between the top of the well, at ground level, and the top of the lubricator wherein the wire is to be fed. It is in this space that both the operational tools and the weights must be attached, and the appropriate connections made.
In order to provide for the introduction of fishing tools and the like in those instances wherein internal pressure makes the use of weights impractical as the sole means for downwardly moving the tool-supporting cable or wire, proposals have been put forth for the use of cable feeding devices which engage and effect a positive downward driving of the cable. The prior art provides for the positive driving of the cable by appropriate drive assemblies or devices which are exemplified in the following patents:
U.S. Pat. No. 2,262,364, Hugel et al, Nov. 11, 1941 PA0 U.S. Pat. No. 2,693,858, Osmun, Nov. 9, 1954.
These known devices include a drive wheel driven, through gear reduction means, either manually as in Osmun, or hydraulically directly from the well pressure as in Hugel et al. In addition, each device includes manual means for adjusting pressure rollers to engage the cable against the drive wheel.
Inasmuch as the patented devices require manual control, it appears that they are specifically intended for installation at ground level with the weights being eliminated. Installation of the patented devices at the upper end of a lubricator, which could extend to a height of from thirty to sixty feet, would be highly impractical in light of the necessity for manual control of the components. Utilizing such feed apparatus as the sole means for introduction of the cable against internal pressure requires substantial pressure on the cable over an extended period of time and noticeable wear on both the device and the cable. This could be particularly troublesome when utilizing cables with internal electrical lines which are susceptible to damage by excessive pressure as might be encountered in the gripping and inwardly feeding of the cable.
The reduction gearing associated with the drives of the patented devices produce a relatively slow cable movement which, while possibly practical when feeding unweighted cable, is time-consuming when attempts are being made to open a shut-down well. Similarly, the drives of the patented devices, concerned with the introduction of cable against internal well pressure, appear to lack a capability of performing any significant control function as the cable is withdrawn.